Cellular plastic foam material such as urethane is often used as a sealing material by attachment of urethane sheet to structural members which are typically made of metal such as steel. An example is an automobile heater bypass door, a fabricated product which includes a metal plate having urethane foam bonded to the opposite faces thereof and a plastic bracket which is riveted to the metal plate to provide a mounting structure as well as a crank connector bracket for moving the door between operative positions.
It is highly desirable from the standpoint of cost and weight savings to replace the metal plate with plastic; i.e., essentially to integrate the metal with the current plastic mounting bracket in not only the above described heater bypass door but in many other products which use plastic foams as a sealing material. However, this means bonding the foam to the plastic structural element. When that structural element is made of polypropylene or certain related rigid plastics, it is difficult or impossible to achieve a satisfactory bond between the plastic and the urethane foam. Accordingly, the metal-plastic composite approach continues to predominate.